In an amperometric enzyme sensor, the background current refers to the small amount of current that exists even in the absence of the analyte that is being measured. This value may be measured in sensors that are specially constructed without enzyme, thus being incapable of a response to an analyte such as glucose or lactate. When such sensors (those lacking an enzyme) have been implanted in animals or in humans, an exemplary background current has been typically between about 0.5 and 2 nA (nanoamperes).
In addition, the accuracy of a glucose biosensor in the hypoglycemic range is quite important from a clinical standpoint. For example, if the true capillary blood glucose is really 65 mg/dl (low) and the sensor estimate is 80 mg/dl, this is a serious error, i.e. true hypoglycemia was missed due to a sensor overestimate. Misdiagnosis of hypoglycemia could lead to coma, seizures, automobile accidents, etc.